There are presently essentially three different approaches for implementing a protection system for circular saw benches and panel sizing saws whose purpose is to prevent a user from coming into contact with a circulating saw blade or from suffering a serious cut wound.
The protection system registered and marketed under the company name Sah Stopp Inc., an American manufacturer, is an emergency braking system that allows the machine tool to be braked in response to a direct engagement of a braking actuator on the saw blade, as soon as a dangerous situation is detected by a sensor designed for that purpose. In this connection, a hot-wire trigger is used to push a rotationally mounted aluminum block with the aid of a pretensioned spring into the tooth system of the running saw blade, wedging it therein and thereby absorbing the rotational energy of all of the machine tool geometries that rotate during the sawing process. This one-sided application of force on the cutting edges has the secondary effect of retracting the saw blade into the saw bench via a structurally specially designed suspension configured on the saw bench. With the aid of this assembly, one is able to prevent serious injury to the machine tool operator who triggers the protective mechanism. The inherent disadvantage here is the direct action exerted on the machining tool, thus on the cutting geometry of the saw blade, since further potential danger is posed to the user by the breaking away of tooth system parts. Moreover, to restore the operability of the protection system, the braking unit, including the saw blade, must be replaced with an operable replacement unit. This must be stocked by the user to allow work to continue once a braking action using the protection function has taken place. This entails substantial follow-up costs and associated time expenditure for procurement and installation. It can also be assumed that all of the components affected by the braking action, i.e., all rotating geometries of the machine tool, are subject to high loads during the deceleration phase. Neither the manufacturer of this system nor relevant publications report data regarding the fatigue strength of the system.
Another approach provides for using a protection system exclusively to lower the saw blade into the saw table without initiating a braking action for the saw blade. In this case, a pyrotechnic priming charge is used to remove the saw blade, including the main shaft and its bearing, from the danger zone, so that serious injury to the user can be prevented. The inherent disadvantage of this type of protection system is that relatively large masses, in the form of assemblies to be lowered, must be moved under strict time stipulations in the millisecond region. The thereby necessitated pyrotechnic igniters, which prove to be indispensable for this type of protection actuator, also entail an expensive reversibility of parts. The capability to immediately continue working on the machine tool using an operable protection system, is hereby limited, both temporally as well as organizationally. Moreover, a limited space and a very specific procedural method make this protection system only suited for relatively large stationary apparatuses, such as circular saw benches, for example, which are able to accommodate such an assembly in the interior thereof. However, this system is eliminated from consideration for a use on smaller manual apparatuses, such as cross-cut and miter saws or panel saws, for example.
A publication from a publicly funded project called “Cut-Stop” (VDI/VDE/IT) for a protection system for panel sizing saws from the Institut für Werkzeugmaschinen (Institute for Machine Tools) (IFW) of the University of Stuttgart describes an approach which employs a special form of a disk brake system, namely a self-energizing wedge brake, to bring the main shaft of the machine tool and thus the saw blade to a standstill. A pyrotechnic igniter is used to accelerate and subsequently push a wedge between a fixed wedge guide in the form of a modified brake caliper and the rotating brake disk. For the selection and combination of specific wedge angles α and brake lining values μ, the assembly has a self-locking effect, so that, depending on the inertia of the mass to be decelerated, the particular time requirements of the braking action can be met by this design. However, even in this case, as described in the mentioned publication, this protection system has the disadvantage that, following triggering of the protection actuator, it is necessary to replace the complete brake unit due to the wedge that is jammed into the friction pairing. The time required to completely restore system readiness is approximately 10-12 minutes for the scope of work to be performed. Thus, it holds in this case as well that the immediate reversibility of the system is somewhat limited.
German Patent Application DE 195 36 995 A1 discusses a safety brake for elevators that has a device which, in response to exceedance of a defined maximum velocity of the conveyance arrangement, brakes the drive at a velocity-dependent deceleration and, if indicated, also stops the same. The safety brake of the German Patent Application DE 195 36 995 A1 acts as a function of the speed directly on the driving disk of the cable-actuated conveyance system and is able to limit the rotational speed thereof. In addition, the safety brake designed as a centrifugal brake has a device for boosting the braking power as a function of the conveying velocity.
Against this background, it is an object of the exemplary embodiments and/or exemplary methods of the present invention to devise a machine tool having an alternative design, a protection system of the machine deploying its protective action very rapidly, in particular within a few milliseconds (typically 1-50 ms), and at least partially resolving the problems described at the outset.